1. Field of the Invention
The present invention relates to a magnetic sensor circuit and a semiconductor device employed in an MI (magneto-impedance effect) sensor for detecting a weak magnetic field.
2. The Description of the Related Art
As a miniature and high-performance magnetic sensor, a magnetic impedance effect sensor (MI sensor) applying magnetic impedance (MI) effect has been proposed. The MI sensor employs a magnetism sensing device and an MI device, and detects magnetic field intensity applied to a soft-magnetic amorphous wire of the MI device. The MI effect corresponds to a phenomenon that, when a pulse current at a short time duration is made to flow through the soft-magnetic amorphous wire, impedance increases in proportion to magnetic field intensity applied to the soft-magnetic amorphous wire.
There is a MI sensor employing an impedance detection system in which the impedance of the soft-magnetic amorphous wire is detected and another MI sensor employing an inductance detection system in which only an inductance component of the soft-magnetic amorphous wire is detected.
In the impendence detection system, since the MI device only requires the amorphous wire, a structure of the MI device is advantageously simple. However, since output characteristics are symmetrical with respect to a zero magnetic field, a direction of a magnetic field should be measured separately, and a circuit configuration becomes complicated for measuring both positive and negative magnetic fields.
On the other hand, in the inductance detection system, a structure of the MI device is rather complicate since a detection coil is wound on the amorphous wire. However, since a linear output can be obtained with respect to positive through negative magnetic fields across a zero magnetic field, a circuit configuration is relatively simple. As a result, a study has been actively made for utilizing such a type of MI device in an electronic compass or such (for example, see Japanese Laid-open Patent Applications Nos. 2004-119517 and 2000-19235, as well as a journal of the magnetic society of Japan, Vol. 27, No. 11, (2003), pages 1063-1068, ‘MI Sensor-based Electronic Compass for Mobile Phone Applications’, written by Y. Honkura, H. Aoyama, M. Yamamoto, and E. Kako).
FIG. 1 shows a circuit diagram of a MI sensor in the related art. As shown in FIG. 1, each of MI devices 101 and 102 measure and output magnetic fields along two axes, i.e., x-axis and y-axis. In this MI sensor 100, a pulse signal generated by a pulse generating circuit 103 is supplied to the x-axis MI device 101 and the y-axis MI device 102 alternately via a timing signal generating circuit 104. Then, detection signals induced in detection coils of the respective MI devices 101 and 102 are held and detected in a sample-and-hold circuit 105, and is amplified and output from a differential amplification circuit 106.
Such an MI sensor is used outdoors in a form in which it is mounted in a portable terminal device such as a cellular phone, an automobile, or such. Therefore, such an environment of the MI sensor is expected as to have a temperature range between a freezing temperature and the order of 40° C.
Therefore, the MI sensor in which a temperature compensation circuit is mounted, so that a detection error in magnetic field intensity is reduced even under a temperature changing environment was proposed(see Japanese Laid-open Patent Application No. 2000-19235).